OBJECTIVE: In this study, we tested the efficacy of bright light therapy as an adjunct to antidepressant treatment (sertraline) in patients with non-seasonal major depression. METHOD: In a randomized double-blind controlled trial, 102 patients were treated for 5 weeks with either white bright light (10.000 lx, 1 h/day) or red dim light (50 lx, 30 min/day). All patients received sertraline in a dosage of 50 mg daily. The self-assessment scales used were the Major Depression Inventory (MDI), the Psychological General Well-Being Scale (PGWB) and the Symptom Check List (SCL-90R). RESULTS: On all three questionnaires the score differences between baseline and endpoint were greatest in the bright light group. On the SCL-90R, the difference reached statistical significance. Results and effect sizes are compared with results from Danish national population studies applying PGWB and SCL-90R. CONCLUSION: The results advocate the use of bright light as an adjunct treatment of non-seasonal depression.